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Grids and Datums THE HELLENIC REPUBLIC

The region of present-day was occu- of hydrographic surveys, became the national national grid was Greece. In 1980, Brigadier pied in the Paleolithic period, and Indo-Eu- grid system of Greece in the 20th century. General Dimitri Zervas, commander of the ropean invasions began about 2000 B.C. An- The Hatt projection is quite similar to the Hellenic Military Geographical Institute, sent cient Greece was never unified, but the city- Azimuthal Equidistant projections used in a treatise to me entitled H AZIMOUQIAKH states of and Sparta dominated while Yemen, Guam, and Micronesia; the differ- ISAPECOUSA PROBOLH TOU HATT , 1963 other cities shifted over the centu- ences are based on the mathematics used to (HATT AZIMUTHAL EQUIDISTANT PROJEC- ries. Alexander the Great conquered most compute the ellipsoidal geodesic for the di- TION). The 21-page tome was written en- of the Mediterranean region and spread rect and inverse cases. Gougenheim, another tirely in Greek by John Bandecas, but Gen- Greek culture throughout the known world. French hydrographic engineer, later pub- eral Zervas mercifully penciled-in English However, Greece was conquered by Rome lished a number of treatises on the geodesic translations of paragraph headings so that I in 146 B.C., and by 1456 A.D. Greece was that were later picked up by Paul D. Thomas could understand the mathematics pre- completely under the Ottoman Turk Empire. who published a treatise for the U.S. Navy sented. That was my one and only experi- Greece won its from on the same subject in the 1970s. Thomas ence with Greek geodesy in which the only in the war of 1821-1829, and celebrates its presented extensive computational proofs thing I could comprehend was the Greek Independence Day on 25 March (1821). The of Gougenheim’s work that established the symbols for standard geodetic terms in the former is now a parlia- standard for “hand and mechanical calcula- math! mentary republic; the was rejected tor” solutions of the geodesic for global ap- Coordinates later published for the Datum F by referendum on 08 December 1974. plications of the U.S. Navy. In the 1980s, Origin were o = 37° 58' 18.680" North and L Greece is slightly larger than the state of Thomas’ work inspired my research partner o = 23° 42' 58.815" East of Greenwich, but Alabama, and it is bordered by curiously the National Topo- (282 km), (494 graphic Series published by the km), Turkey (206 km), and Hatt was the hydrographer of the French Greek Military used the Athens (246 km). The low- Observatory as their national est point in Greece is the Medi- Navy, and later taught at a university in Paris. prime meridian. The map series terranean Sea, and the highest Apparently he made quite an impression on at various scales were based on point is (2,917 a Greek student because the Hatt projection, integer minute differences from m). the Athens meridian. The basic In 1889, the Greek Army Geo- used by the French Navy for local grids of series were based on 30- by 30- graphical Service was formed, hydrographic surveys, became the national minute blocks with latitudes of and classical triangulation com- grid system of Greece in the 20th century. 36° 30' N to 42° 00' N and longi- menced immediately. The tudes of 4° 30' W of Athens to agency name was later changed 3° 30' E of Athens (23° 42' to the Hellenic Military Geographical Ser- at the University of New Orleans, Dr. Michael 58.815" East of Greenwich). vice (HMGS). The initial starting point for E. Pittman, to publish his original solution of The “Revised Military Grid” used in some the triangulation was the Old Athens Ob- the “Principal Problem of Geodesy” in the national applications after WWII was based F servatory where o = 37° 58' 20.1" North, Surveying and Mapping journal of the ACSM. on the Lambert Conformal Conic projection. L o = 23° 42' 58.5" East of Greenwich, and The other projection variants mentioned Using the same central meridian as the Ath- was referenced to the Bessel 1841 ellipsoid above for Yemen and Guam used the ellip- ens Observatory, the three tangent zones where the semi-major axis a = 6,377,397 soidal geodesic solutions developed by Puis- had latitudes of origin of 35°, 38°, and 41° 155 meters and the reciprocal of flattening sant and by Andoyer-Lambert. The Azimuthal with False Eastings of 1,500 km, 2,500 km, 1/f = 299.1528128. The Yeografikí Ipiresía Equidistant for Micronesia was developed and 3, 500 km, respectively, and all three Stratoú map series at 1:20,000 scale was by the late John P. Snyder using the “Clarke zones had False Northings of 500 km. The produced from 1926 through 1947, and had Long Line Formula” originally developed by “Old Military Grid” used from 1931 to 1941 the Greek Military Grid shown on some Colonel A. R. Clarke of the British Royal En- had the same parameters except that there sheets. The series covered the northern gineers (PE&RS, February 1999). Hatt’s pro- were no false origins. border and scattered strategic areas through- jection was an enormous influence on Euro- From 1925 to 1946, there were two “Brit- out Greece. The Greek Military Grid was pean cartography world-wide for many de- ish Grids” used by the Allied Forces. The based on the Hatt Azimuthal Equidistant pro- cades, and I am often amused to see con- Mediterranean Zone was a secant Lambert jection, a system originally presented on the temporary software packages list unknown Conical Orthomorphic where the central me- sphere by Guillaumme Postel. projections and grid systems as “Systémé ridian was 29° East of Greenwich, and the Hatt was the hydrographer of the French Rectangulaire Usuel” with no further infor- latitude of origin was 39° 30' N, the scale Navy, and later taught at a university in Paris. mation. That “Usual Rectangular System” factor at origin was 0.99906, the False Easting Apparently he made quite an impression on found worldwide is the Hatt projection! Nev- was 900 km, and the False Northing was 600 a Greek student because the Hatt projec- ertheless, the only country that adopted the km. The Zone was a tangent Lambert tion, used by the French Navy for local grids Hatt Azimuthal Equidistant projection as the continued on page 1238

PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING December 2002 1237 Grids and Datums

continued from page 1237 Conical Orthomorphic where the central meridian was Athens (24° 59' 40" East of Greenwich), the latitude of origin was 35° N, the scale factor at origin was 1.0 (by definition of a tangent zone), the False Easting was 200 km, and the False Northing was 100 km. There is a new reference system used in Greece nowadays. It is called the Greek Geodetic Reference System of 1987 (GGRS87) F L where o = 38° 04' 33.8107" North, o = 23° 55' 51.0095" East of

Greenwich, No = 7.0 m, and the new Greek Grid is based on the Transverse Mercator projection (presumably Gauss-Krüger) where f l o = 0°, o = 24° E, the False Easting = 500 km, and the scale factor at

origin (mo) = 0.9996. Generally, I have serious doubts concerning any “new” grid system that uses some non-standard variant of the UTM Grid, but I understand that this particular one was devised by Profes- sor Veis of the Technical University of Athens. If Professor Veis ap- proved of this new grid, then there certainly must be a valid techni- cal reason for the curious parameters chosen. Thanks for the above parameters go to Yannis Yanniris, a photogrammetrist in Athens. The National Imagery and Mapping Agency (NIMA) has published datum shift parameters from the European Datum of 1950 in Greece to the WGS84 Datum where DX = –84 m, DY = –95 m, and DZ = –130 m; however, this solution is based on only two points and the accu- racy of the components is stated to be ±25 m. Users interested in geodetic applications of GPS in Greece should read the NIMA notice published next to my column in PE&RS October, 2002. The European Petroleum Studies Group has published shift parameters from GGRS87 to WGS84 as being DX = –199.87 m, DY = +74.79 m, and DZ = +246.62 m. The EPSG published no accuracy estimates for their parameters, so caveat emptor. ò Cliff Mugnier teaches Surveying, Geodesy, and Photogrammetry at Louisiana State University. He is the Chief of Geodesy at LSU’s Cen- ter for GeoInformatics (Dept. of Civil and Environmental Engineer- ing), and his geodetic research is mainly in the subsidence of Louisi- ana and in Grids and Datums of the world. He is a Board-certified Photogrammetrist and Mapping Scientist (GIS/LIS), and he has ex- tensive experience in the practice of Forensic Photogrammetry.

The contents of this column reflect the views of the author, who is responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the American Society for Photogrammetry and Remote Sensing and/or the Louisiana State University Center for GeoInfor- matics (C4G).

1238 December 2002 PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING